Examples of a biometric authentication technique include “1:1 authentication” and “1:N authentication.” The 1:1 authentication refers to a method that performs authentication by comparing biometric information input by a user and biometric information registered in advance in association with the identification information of the user. The 1:N authentication refers to a method that performs authentication by comparing biometric information input by a user and the biometric information of N people registered in advance. When the 1:N authentication is employed, because the biometric data input by the user is compared with the biometric data of N people registered in advance, a lager registration number N of biometric data requires more time to output an authentication result.
Examples of a technique that reduces authentication time in the 1:N authentication include a fingerprint comparison apparatus that compares selection parameters representing feature quantities of fingerprints between an input fingerprint and registered fingerprints, thereby narrowing down the registered fingerprints to be compared with the input fingerprint. In this fingerprint comparison apparatus, the selection parameters are compared before comparison, which include the ratio of a ridge area with respect to the entire fingerprint area, the space between a ridge and a valley, and the number of endpoints and bifurcations that a ridge or valley of a fingerprint has.
Patent Literature 1: Japanese Patent Application Laid-open No. 2004-145447
However, the above-mentioned prior art is problematic in that the accuracy of narrowing down is not stable as will be described below.
Specifically, the above-mentioned fingerprint comparison apparatus performs narrowing down on the precondition that the fingerprint does not change for the same user between the time when the fingerprint was registered and the time when the fingerprint is used for authentication. It is difficult for the above-mentioned fingerprint comparison apparatus to cope with narrowing down when a temporary change occurs in a living body due to a scratch, chapping, or the like, because when the temporary change occurs in a fingerprint due to a scratch, chapping, or the like, a difference in a selection parameter to be compared between an input fingerprint and registered fingerprints increases even if the fingerprint is of the same user. In the above-mentioned fingerprint comparison apparatus, therefore, even when the registered fingerprints are narrowed down by comparing the selection parameters between the input fingerprint and the registered fingerprints, the registered fingerprint of the user is not always included in the registered fingerprints that are obtained as a narrowing-down result, and are compared with the input fingerprint.